Hitherto, various studies have been conducted on the improvement of wet performance of a pneumatic radial tire for a motorcycle. In particular, as a technology for improving the wet performance by improving a tread pattern, it has been known that lug grooves have to be distributed in a shape of chevron with respect to an advancing direction to enhance a hydroplaning performance. Meanwhile, it is necessary to bring out an edge effect by distributing the lug grooves in a shape of reversed chevron with respect to the advancing direction in order to assure a wet traction performance.
However, it has been pointed out that safety in running is lost if the lug grooves are additionally distributed in the shape of reversed chevron that brings out the edge effect for obtaining the wet traction performance to the lug grooves distributed in the shape of chevron to meet the two kinds of wet performances in the same time because uniformity of rigidity balance is lost and linearity in handling drops in a process of turning from straight running.
As a technology for improving the tread pattern of a motorcycle tire, Patent Document 1 describes a pneumatic radial tire for a motorcycle in which a set of right and left lug groove patterns is formed into a shape of reversed W as a whole with respect to a tire rolling direction, regions where right and left intermediate bending points P of the reversed W are positioned in a predetermined range of a half-width TW of developed tire from a center circumference of the tire and angles of lug groove components near a tire shoulder portion from the bending point P and near the tire center circumferential line form predetermined angles respectively with respect to an equator of the tire. Patent Documents 2 through 4 also describe technologies for improving performances of motorcycle tires by improving tread patterns.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 10-297218 (Claims and others)
Patent Document 2: Japanese Unexamined Patent Application Publication No. 6-55909 (Claims and others)
Patent Document 3: Japanese Unexamined Patent Application Publication No. 3-135802 (Claims and others)
Patent Document 4: Japanese Unexamined Patent Application Publication No. 63-121505 (Claims and others)